Properties of the escape system of cockroaches during walking

1. Adult male cockroaches (Periplaneta americana) which were fixed in place but could move their legs normally were presented with wind puffs of different amplitudes. The puffs were given while the cockroaches were walking at different speeds, standing or grooming their antennae. In different experiments we recorded either the movement responses of one metathoracic leg or the action potentials from impaled, individually identified giant interneurons. 2. Cockroaches were most responsive behaviorally to wind puffs presented during slow walking (1-4 steps/s). At such times the latency was shortest (11-18 ms for large puffs) and the threshold lowest (Fig. 2). The threshold wind puff, having a peak velocity of 3 mm/s, evoked a pause in walking. Puffs of 12 mm/s or larger evoked running. 3. The ventral giant interneurons (GI's) though known to be inhibited slightly during slow walking (Daley and Delcomyn 1980 a) are still activated by wind puffs of 3 or 12 mm/s (Fig. 3) and thus can contribute to the behaviors that these small wind stimuli evoke. Pronounced inhibition of the ventral GI's occurred only during fast walking (Fig. 4). The dorsal GI's appear to be insufficiently activated by these small winds to contribute to the havior. 4. In response to large wind puffs presented during slow walking, the behavioral latency is so short that only a few action potentials of the largest ventral GI's appear to be capable of mediating the onset of the behavior. The dorsal GI's appear to be activated too late to contribute to initiating the behavior. 5. The information suggesting that the ventral, and not the dorsal GI's initiate the escape behavior has permitted us to develop a coherent model of the escape system in which all the known synaptic interactions involving both the ventral and the dorsal GI's have a meaningful role (Fig. 5). The model includes negative feedback onto the ventral GI's and positive feedback onto the dorsal GI's from the motor system. According to this model, the ventral GI's initiate and steer the early part of the escape behavior, and the dorsal GI's maintain and steer the subsequent phases of the behavior.